A metal structure, built as a single unit having a fixed length or composed of two or more units adjustable to various lengths, designed for attaching to a crane or crane-shovel basic unit, the top being fitted with one or more sheaves through which wire ropes are passed to raise or lower a hook, various types of buckets, grapples or other attachments in conjunction with the crane or crane-shovel basic unit when used in excavation or material handling operations.